Macromolecular engineering using commodity monomers is becoming a major trend in polymer technology to satisfy the demand for new properties, improved cost effectiveness, ecology and quality. Functional polymers with low molecular weight, low polydispersity, compact, branched structures and terminally-located reactive groups are expected to exhibit superior performance/cost characteristics, by virtue of lower inherent viscosity and higher reactivity vs. conventional linear statistical copolymers.
The terminally-functional branched polymers appear to be ultimate reactive substrates for networks, because the branch points can substitute for a significant portion of expensive reactive groups and provide better distribution of the reactive groups. Polymers having large numbers of short branches below critical molecular weight are unlikely to form any entanglements and should exhibit low inherent viscosity and good flow even in concentrated solutions.
Conventional techniques for synthesizing well-defined branched polymers require expensive multistep processes involving isolation of reactive intermediate macromonomers. The macromonomers have polymerizable end groups, which are usually introduced using functional initiator, terminating or chain transfer agent. Well-defined branched polymers are prepared by the macromonomer homopolymerization or copolymerization with suitable low molecular weight comonomer selected based on known reactivity ratios. These methods have been reviewed and only single-branch polymers from single incorporation of the macromonomers are reported; multiple reincorporation of the growing macromonomers was never attempted, e.g., R. Milkovich, et al., U.S. Pat. No. 3,786,116; P. Remp, et al., Advan. Polymer Sci., 58, 1 (1984); J. C. Salamone, ed., Polymeric Materials Encyclopedia, Vol.3 and 4 (1996).
Several linear macromonomers were prepared by end-capping of living anionic polyolefins with unsaturated terminating agents providing polymerizable olefin end-groups, e.g., R. Asami et al., Macromolecules, 16, 628 (1983). Certain macromonomers have been incorporated into simple graft polymers by homo- or copolymerization with branched structure not well-characterized and reincorporation of the macromonomers into more complex structures was not considered.
Dendrimers or hyperbranched polymers are conventionally prepared using expensive, special multifunctional monomers or expensive multistep methods requiring repetitive isolation of the reactive intermediates. Nothing in the prior art discloses synthetic conditions for production of macromonomers or polymers containing branches upon branches.
This invention relates to a general process for the synthesis of polyolefins containing branches upon branches and having polymerizable olefin end groups by a convenient one-pot polymerization of selected vinyl monomers with chain polymerization initiators and a method to provide olefin end groups by chain termination agents. The polymerization is carried out in such a manner that chain termination occurs gradually and each chain termination event terminates that particular polymer chain with polymerizable olefinic functionality. Subsequent reincorporation of the linear polymer chains produced early in the reaction leads to branching of subsequently-formed macromolecules which are terminated with polymerizable olefinic functionality. Subsequent reincorporation of the branched macromolecules leads to subsequently-formed polymer molecules containing branches upon branches which are terminated with polymerizable olefinic functionality. Spontaneous repetition of the process leads to highly branched or hyperbranched dendritic products still retaining polymerizable olefinic termini.
This invention concerns an improved process for the anionic polymerization of at least one vinylic monomer to form a branched polymer comprising contacting, in the presence of an anionic initiator:
(i) one or more anionically polymerizable vinylic monomers having the formula CH2xe2x95x90CYZ, and
(ii) an anionic polymerization chain terminating agent of formula CH2xe2x95x90CZxe2x80x94Qxe2x80x94X,
wherein:
Q is selected from the group consisting of a covalent bond, xe2x80x94Rxe2x80x2xe2x80x94, xe2x80x94C(O)xe2x80x94, and xe2x80x94Rxe2x80x2C(O)xe2x80x94;
Y is selected from the group consisting of R, CO2R, CN, and NR2;
X is selected from the group consisting of halogen, and RSO3;
Z is selected from the group consisting H, R, and CN;
R is selected from the group consisting of unsubstituted and substituted alkyl, vinyl, aryl, aralkyl, alkaryl and organosilanyl groups and Rxe2x80x2 is selected from the group consisting of substituted or unsubstituted alkylene, arylene, aralkylene, alkarylene and organosilanylene groups; the substituents being the same or different and selected from the group consisting of carboxylic acid, carboxylic ester, hydroxyl, alkoxy and amino;
where acidic protons, if any, can be protected from example by organosilanyl, tertiary alkyl or benzyl;
wherein the improvement comprises obtaining higher yields of branched polymer, the polymer having dense branch upon branch architecture and polymerizable vinylic chain termini, employing steps I, III, VI and at least one of II, IV and V:
I. reacting (i) with an anionic initiator in a first step:
II. decreasing the ratio of (i) to anionic initiator toward 1;
III. adding (ii) optionally with some (i) in a second step;
IV. selecting the rate of the (ii) addition, dependent on the (ii) reactivity;
V. increasing the ratio of (ii) to anionic initiator toward 1; and
VI. increasing the conversion of (i), (ii) and olefinic end groups from 70 to 100%.
Based on the disclosure and Examples presented herein, one skilled in the art can select the optimum steps I-VII with minimum experimentation. One skilled in the art will also be able to select the appropriate anionic initiator and chain transfer agent for the monomer(s) being polymerized, by reference to the well-known conditions for anionic polymerization. Optionally, the process includes the step, VII, of converting anionic-growing end groups into non-polymerizable end groups. It is preferred to operate process step V at a ratio of about 0.7 to 1, most preferably from 0.8 to 1. In step IV, the rate of addition will vary in the same direction as reactivity of (ii) so that addition will be relatively slow for less reactive component (ii) and will increase commensurate with increased reactivity of component (ii).
This invention further concerns the product of the above reaction which is composed primarily of a polymer having a branch-upon-branch structure and a polymerizable olefinic end group, having the structure: 
Bxe2x80x2=Z, B;
n=1-100, m=0-50, p=0-100, n+m+pxe2x89xa72;
if m greater than 1, then the m insertions are consecutive or not consecutive;
A=anionic initiator moiety selected from the group consisting of R; and
Q, Y, Z are as earlier defined.
Branch-upon-branch polymers (BUBP) are superior over straight branch polymers (SBP) in terms of more compact structure, reflected in lower inherent viscosity and better flow properties in melts and solutions for any given molecular weight of polymers. Therefore, BUBPs require less solvents and lower temperature than SBPs for processing.
BUBPs with terminal end groups are superior over SBP substrates by having much larger network fragments, which can be preformed and incorporated into new topology networks. BUBPs allow formation of new types of hybrid networks by combining different BUBPs with a good control on molecular level.
BUBPs allow incorporation of larger numbers of branch points per macromolecule, which are equivalent to curing sites. This improves economy and conversion of reactive coatings by reducing the number of expensive curing sites.
In general, BUBPs offer at least a 10 percent improvement over SBPs of the same molecular weight in such characteristics as lower viscosity, reduced need for solvent, fewer curing sites in reactive substrates for networks and higher conversion of curing sites in final coatings, all of which provide better product stability.
We have discovered a process for the synthesis of polyolefins containing branches upon branches and having polymerizable olefin end groups by a convenient one-pot polymerization of selected vinyl monomers with chain polymerization initiators and a method to provide olefin end groups by chain-termination agents. The polymerization is carried out in such a manner that chain termination occurs gradually and each chain-termination event terminates that particular polymer chain with polymerizable olefinic functionality. The process is shown in Scheme 1. 
Subsequent incorporation of the linear polymer chains 1 produced early in the reaction leads to branching of subsequently-formed macromolecules terminated with polymerizable olefinic functionality 2. Subsequent reincorporation of the branched macromolecules 2 leads to polymer molecules containing branches upon branches 3 which are terminated with polymerizable olefinic functionality. Spontaneous repetition of the process leads to highly branched or hyperbranched dendritic products still retaining polymerizable olefinic termini.
The polymers made by the present process are useful in a wide variety of applications including coatings, processing aids in extrusion, cast, blown or spray applications in fiber, film, sheet, composite materials, multilayer coatings, photopolymerizable materials, photoresists, surface active agents, dispersants, adhesives, adhesion promoters, compatibilizers and others. End products taking advantage of available characteristics, particularly low inherent viscosity, can include automotive and architectural coatings having high solids, aqueous- or solvent-based finishes.
In a preferred process, the anionic initiator is selected from alkali metals, radical anions, alkyllithium and other organometallic initiating compounds, ester enolates, functionalized initiators, typical examples of which include: butyl-, methyl-, isopropyl-, phenyl-, vinyl-, allyl-lithiums, cumyl potassium, fluorenyl lithium.
Chain termination agents include p-vinylbenzyl chloride and bromide, p-vinylbenzyl tosylate, allyl chloride and bromide, vinyldimethylchlorosilane, vinyl(chloromethyl)dimethylsilane, p-vinylphenyldimethylchlorosilane, methacryloyl chloride.
Substituents Q and X of the chain terminating agent are chosen to convey the appropriate reactivity in the terminating step and in anionic copolymerization of the desired monomer(s) under polymerization conditions.
The process can be conducted by bulk, solution, suspension or emulsion polymerization using batch or preferably starved feed reactor, which offers better process control.
The treelike dendritic branched polymers are formed by in situ generation and copolymerization of first linear and subsequently increasingly branched macromonomers through the polymerizable olefin group (Scheme 1). The method can be employed in anionic polymerization of styrene initiated by alkyllithiums, where dendritic structures are formed by continuous addition of vinylbenzyl halides and/or vinylchlorosilanes acting as chain terminating/functionalizing/branching agents (Scheme 2). The data are consistent with a mechanism, in which the initially-formed linear macromolecules receive predominantly the vinyl end group through the termination by the vinylbenzylhalide or vinylchlorosilane. The vinyl reactive end group allows the linear macromonomer to participate in analogous subsequent (secondary) copolymerization steps leading eventually to even more branched structures (xe2x80x9cbranch upon branchxe2x80x9d or dendrigrafts). 
Polystyrenes with molecular weights in the range 3,000-60,000, polydispersity  less than 2.5 with 5 to 40 branches, each containing 3 to 30 monomer units were prepared, primarily controlled by the initiator/monomer/chain terminating agent ratio, relative addition rates, the reactivity ratios of the macromonomer and (co)monomers.
A chain polymerization is controlled by a chain termination step so as to provide a polymerizable olefin end group (Scheme 1). The branch upon branch structure is build by in situ generation and copolymerization of linear and subsequently increasingly branched macromonomers through the polymerizable olefinic group.
The monomer copolymerizability of CH2xe2x95x90CYZ primarily determined by the steric and electronic properties is well documented in the art. The chain process can involve either one or several different comonomers and is preferably anionic but can also be cationic or radical. Typical monomers include monoolefins, preferably styrene, a-methyl styrene, substituted styrenes, substituted styrenes with protected functional groups, vinyl aromatics, vinylpyridines, conjugated dienes, vinyl silanes, acrylates, methacrylates, acrylonitrile, vinylidene cyanide, alkyl cyanoacrylates, methacrylonitrile, vinyl phenyl sulfoxide, vinyl aldehydes, vinyl ketones and nitroethylenes.
The data are consistent with a mechanism, in which the initially-formed branched macromolecules 2 receive predominantly the olefin end group through the chain termination. See Scheme 1. Having a reactive olefin end group allows 2 to participate in analogous subsequent (secondary) copolymerization steps leading eventually to branch-upon-branch polymers, 3.
Formation of branch-upon-branch structures 3 is indicated by the significant increase (up to 50xc3x97) in the polymer molecular weight compared to the control experiments where the same monomer/initiator ratios but nonolefin chain terminating agents such as benzyl chloride or methanol are used instead of the p-vinylbenzyl chloride.
In general, vinylsilane terminated macromonomers show much lower reactivities toward homo- and co-polymerizations under the conditions studied, leading to polymers with lower molecular weight and less branched structures.
Branched structures of copolymers 3 are confirmed by very low inherent viscosities, values of xe2x80x9caxe2x80x9d coefficient in Mark-Houwink equation, [xcex7]=K Ma, falling in the range 0.18-0.66 vs. 0.72 for linear polystyrenes, branching factors approaching 0.4 and the RMS radius less than a half of the linear analog of the same molecular weight in the range 105-106 as measured by GPC with a dual RI/LS detector.